This invention relates to the continuous casting of metals, especially of copper or copper alloys in the form of billets or slabs.
In one process for the continuous casting of copper slabs or billets, molten copper is continuously fed into a water-cooled, graphite-lined mould from which the cast copper, known as "a strand", issues in a downward direction. The mould is reciprocated vertically during casting to free the moulded copper from the sides of the mould and at the same time the strand is moved downwardly at an appropriate rate, and is supported, by a pair of spring-loaded pinch rolls mounted below the mould on horizontal drive shafts. The strand is then cut, for example by means of a flying saw, into desired lengths typically between 500 and 3 000 mm.
In order that the maximum utilization of equipment is made it is normally advantageous to cast as much material at the same time as can be arranged with the equipment available. Thus the maximum quantity of material can be cast when the strand is in the form of a rectangular cross-sectional slab which has as large a size as possible given the overall dimensions of the machine. In certain cases, however, it is desirable to cast circular cross-sectional strands, normally referred to as billets. The normal method adopted in such an arrangement is to replace the slab mould with a billet mould having two apertures which fit within the cross-section of the largest slab mould so that the billets can be cut by the flying saw normally used to cut the slabs. It is conventionally arranged, with one typical continuous casting machine, that there is provided an assembly comprising four pinch rolls. Two pairs of rolls are used when two strands are being cast simultaneously and only a single pair is used when a slab is being cast. The rolls are movable laterally with respect to the descending strand of cast material and can be forced into contact with the strand or strands to support it and guide it during its downward movement.
In certain circumstances it is required to cast relatively small diameter billets. If small diameter moulds are used then the casting rate is reduced-- the casting rate being limited by the solidification rate of the metal within the moulds. Because it is necessary to support each strand with a separate pair of pinch rolls, the present arrangement of continuous casting machines utilising four pinch rolls is limited to casting a maximum of two billets irrespective of the diameter of the billets.
In an article in November 1977 edition of Metallurgist and Materials Technologist we disclose means whereby existing single and twin strand continuous casting machines can relatively quickly and easily be converted into three strand casting machines. As will be appreciated, in addition to modifying the pinch rollers as is disclosed in those applications, it is necessary to modify other parts of the machine, inter alia the mould and the clamp(s) used to clamp the strand(s) while the latter are cut into manageable lengths.
The clamps are conventionally mounted on a flying saw platform, that is to say a platform having mounted on it a horizontal circular saw blade which is moved laterally, while rotating, to cut through the strand or simultaneously through all the strands. At the same time, the platform, and hence the saw, move downwards at a rate equal to the rate of casting of the strand(s). After cutting has been completed, the saw blade is retracted and the platform is raised to its original position in preparation for the next sawing cycle. The clamps serve to clamp the strand(s) rigidly relative to the saw blade during sawing. After sawing, the clamps are released and each strand is fed downwardly to a downender comprising clamps which rotate the strand(s) from a vertical position into a horizontal position. Each strand is then transported away on a conveyor system.
In single strand casting, the clamps conventionally comprise a pair of opposed jaws which, during sawing, are urged under hydraulic pressure into contact with the strand. As already described, a single strand machine can usually readily be modified into a twin strand, for example billet, casting machine. This entails, inter alia, positioning a pair of clamping rolls, whose axes are spatially fixed, between the pair of opposed jaws, the latter, in the case of billet casting, being V-shaped. During sawing, one strand is clamped between one of the jaws and one of the clamping rolls and the other strand between the order of the jaws and the other of the rolls. The clamping force on the strands is, as in the case of single strand casting, determined by the hydraulic force applied to the jaws. Usually, the strand or strands are clamped below and above the saw line by a pair of clamp arrangements, each of the type just described.
For use in continuously casting three strands, for example billets, in a line we have devised a clamp arrangement which can utilise the existing jaws of a single or twin billet sawing device and which ensures that all three strands are adequately clamped during sawing. The arrangement may, however, be constructed to cope with two strands or more than three strands.